Micro surgical cutting instruments

ABSTRACT

The present invention relates to methods and apparatus for micro surgical blades, knives and assemblies.

This application is a continuation of International Application No.PCT/US2006/061459 filed Dec. 1, 2006 which is a non-provisional of U.S.Provisional Application No. 60/741,200 entitled Micro Surgical CuttingInstruments, filed on Dec. 1, 2005, the entirety of which areincorporated by reference herein.

FIELD OF THE INVENTION

The present invention relates to methods and apparatus for microsurgical blades, knives and assemblies.

BACKGROUND OF THE INVENTION

Conventional metal, diamond tipped or other similar type knives haveblade edges or cutting surfaces that are considerably large when viewedon an atomic scale. Typically such knives have cutting edges rangingfrom 500 angstroms to about 1000 angstroms. Typically, such knivesprovide poor surgical precision and cause unnecessary destruction oftissue when viewed at the cellular level.

Presently, atomic force microscopy uses devices having atomicallysharp-tips for the manipulation and separation of cells. Such devicesand methods are found in U.S. Pat. Nos. 5,221,415; 5,399,232; and5,994,160 the entirety of each of which are incorporated by referenceherein. Additional information regarding devices used in atomic forcemicroscopy may be found in Journal of Nanoscience and Nanotechnology2002, V 2, No. 1, pp 55-59, and Journal of MicroelectromechanicalSystems V 6, No. 4, December 1997, pp. 303-306 the entirety of which arealso both incorporated by reference herein.

References describing the fabrication of micro knives from singlecrystal silicon include U.S. Pat. Nos. 5,728,089; 5,317,938; 5,579,583;5,792,137; 5,842,387; 5,928,161; 5,944,717; 5,980,518; 6,319,474;6,615,496; 6,706,203; and U.S. patent application Nos. 200210078576;200310208911; 200510132581; and 200510144789 the entirety of each ofwhich is incorporated by reference herein. Most conventionalmicro-knives rely on silicon as the cutting blade. Problems may beencountered as silicon is too soft to provide a satisfactory cuttingsurface. As a result, silicon tends to dull quickly. Moreover, siliconis not transparent to visible light so it is not suitable forapplications where it is desirable to see through the blade for precisealignment to the object to be cut.

Accordingly, there remains a need for an improved microsurgical cuttinginstrument.

SUMMARY OF THE INVENTION

The devices and method described herein teach micro-machined blades,knives and cutting instruments. Such micro-machined devices areatomically sharp as described below. Such a construction providesprecise cutting of tissue while minimizing collateral damage to tissues.

In typical applications, a micro-machined blade or micro-knife undergoesan application of a small force. Such a force may be the amount of forcenecessary to separate cells (e.g., less than 10 millinewtons). Thereforewhen cutting tissue with a micro-knife, the drag force applied to theknife must be minimized. In those devices used to cut a single cell in apetri dish there is no significant, drag because the contact area isvery small (only one cell). In contrast when a micro-knife cuts tissuehaving many cells, designing the knife to be as thin as possibleminimizes the resulting drag force exerted upon the knife. Accordingly,unlike conventional thicker knives a thin micro-knife does not pushtissue very far in a lateral direction. Also, the depth of the initialcut caused by a micro-knife is not very deep. The depth of cut istypically, but not limited to applications where cutting is shallow(e.g., less than 1 mm). Exceeding a depth of cut more than about 20times the width of the blade of the micro-knife may increase the risk ofbreaking the blade. Naturally, micro-knife blades shall be optimized fordifferent applications. For example, for cutting 20 microns deep, a 1micron wide blade may suffice. For cutting 1,000 microns deep, a 50micron wide blade may be preferred.

For cutting single cells on the bottom of a petri dish, the width of thebase of a blade can be several hundred microns wide to allow visualtransparency with a microscope. This feature permits alignment of thecutting edge with the target cell. In such a case, drag force doesn'tplay a role since the depth of cut is exactly one cell regardless of thewidth of the blade.

These cutting instruments are useful in the area of microsurgery,including surgery performed on single cells. The surface is smooth onthe atomic scale, and the cutting edge is sharp on the atomic scale(e.g., radius of curvature less than 500 angstroms, with some variationsof the invention ranging between 200 angstroms and 5 angstroms.)

When combined with a rigid filler material, variations of inventivemicro-machined blades may be fabricated to have a knife surface or shell(or body shell, blade surface, cutting surface etc.) with the fillermaterial partially or totally reinforcing the knife surface. As usedherein, the knife surface, blade surface, or cutting surface refers tothe exterior of a shell or similar structure that may be supported witha filler material. Typically, the structure is a shell, but otherconfigurations may be included. For example, the shell may have openingsplaced therein where such openings do not interfere with the cuttingedge formed by the shell.

This reinforced shell configuration permits fabrication of micro-kniveshaving radii of curvature between 5-50 angstroms. As noted above, suchradii are significantly less than conventional micro-blades. However, asnoted above, variations of the invention include knives with radii ofcurvature up to 500 angstrom. The reinforcement provided by the rigidfiller material prevents the blade surface from deflecting and/orbending that would otherwise crack the blade surface. In most variationsof the device, the smoothness of the blade allows the blade to actuallycontact the object to be cut. There are no gaps or aberrations inroughness where a cell may be missed by the cutting edge. The smallradius of curvature of the cutting edge allows for a small cuttingforce. It follows that cutting of cells occurs without tearing orotherwise damaging the cells. It is also noted that knives fabricated bythe disclosed process will have a cutting edge (or outer shell cuttingedge) having a radius of curvature that is less than or equal to aradius of curvature of an adjacent edge of the body portion. Thisconstruction is possible mainly due to the fact that the cutting edge orouter edge is deposited first. Then the body portion is deposited withinthe cutting edge.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a basic wafer assembly.

FIG. 2 illustrates the wafer assembly after a layer of silicon dioxideis applied.

FIGS. 3 and 4 illustrate placement of a photoresist layer and patterningthe photoresist layer respectively.

FIG. 5 illustrates etching through the patterned photoresist layer topattern the silicon dioxide layer.

FIGS. 6 and 7 illustrate removal of the photoresist layer and etching aknife channel into the wafer assembly respectively.

FIG. 8 illustrates removal of the oxide layer.

FIG. 9 illustrates an optional step of placing a sharpening layer on thewafer assembly.

FIG. 10A illustrates placing an exterior knife surface into the etchedwafer.

FIGS. 10B-10C illustrate previous devices in comparison to the presentdevices where a radius of curvature of an exterior shell is less than orequal to a radius of curvature of an interior edge.

FIGS. 11 and 12 illustrate placement of a body portion into the exteriorknife surface and placement of a wafer on the body portion.

FIGS. 13-18 illustrate processing of the wafer assembly to remove thefabricated knife blade.

FIGS. 19A-20 illustrate examples of a knife blade according to thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 to 18 and the accompanying text illustrate one possible methodof manufacturing a micro machined device according to a variation of thepresent invention. It will be appreciated that variations of thefollowing example are within the scope of the invention.

FIG. 1 shows the start of a wafer assembly 1 as being a cross section ofa (100) single crystal silicon wafer 10 that will be used to form themold for the knife.

FIG. 2 shows a cross section of the wafer assembly 1 comprising the(100) single crystal silicon wafer with a layer of silicon dioxide 12grown on it. Typically the silicon dioxide layer 12 is about 1 micronthick, and is grown at 1100 degrees C. in oxygen with steam present.

FIG. 3 shows the addition of a layer of photoresist 14 applied over thesilicon dioxide layer 12. The photoresist 14 may be applied in a numberof ways (e.g., spin applied over the oxide layer.)

FIG. 4 illustrates the photoresist once patterned to reveal exposedareas 16 for etching. Typically, the exposed areas 16 are rectangular inshape to allow for the length of the blade. Although the figureillustrates a single area being exposed, the procedure can includeexposing multiple areas on the assembly 1.

FIG. 5 shows the assembly after etching away of the silicon dioxidelayer 14 that was previously exposed during patterning of thephotoresist. This step exposes the single crystal silicon 10. Typically,etching of the silicon dioxide layer 12 occurs by using aqueoushydrofluoric acid/ammonium fluoride solution) to expose the underlyingsilicon.

As shown in FIG. 6, the photoresist is removed leaving the pattern inthe silicon dioxide layer 12 on the single crystal silicon 10.

FIG. 7 illustrates the assembly after etching of the knife mold pits 18.In one example, the knife mold pits 18 may be etched in the singlecrystal silicon 10 by using aqueous potassium hydroxide (e.g., using 40wt % KOH in water, at 60 degrees C.).

Once the knife mold pits 18 are etched, the remaining oxide layer isremoved (e.g., using concentrated HF). This process leaves a pattern ofan elongate channel 18 within the substrates or wafer 10 material.

FIG. 9 shows the performance of an optional “oxidation sharpening” stepallowing for improved control in the overall manufactured knife. In sucha step, about 0.1 micron of a sharpening layer 20, (e.g., silicondioxide) is grown in dry oxygen at a temperature that may range fromabout 900 to about 950 degrees C. This process allows fine control ofthe sidewall slope at the cutting edge.

FIG. 10A illustrates the formation of an exterior knife surface on thewafer assembly 1. In this example a film of silicon nitride 22 isdeposited on the wafer assembly 1. As noted herein, other materials canbe used in place of silicon nitride. In any case, the deposited filmforms a shell structure 22 in the wafer assembly 1. As shown below, theinterior knife body will be deposited within the exterior knife shell22.

Fabrication of the knife in this manner, namely that the interior knifebody is deposited within the shell created by the exterior knifesurface, allows for smaller sizes when creating the blade edge of theexterior knife shell 22. As the blade edge radius of curvature is alwaysless than a radius of curvature of an edge formed by the filler body 24.In this construction, the filler body reinforces the existing exteriorknife shell 22. If the exterior knife shell were deposited on aninterior filler body, then the blade edge would be greater than acorresponding edge of the filler material.

FIGS. 10B to 10C illustrate this distinction. FIG. 10B shows a blade 120where the interior material 122 is coated with an exterior layer 124,Since the exterior layer 124 is deposited upon the interior material122, the dimension of the blade grows as shown by arrows 126.Accordingly, the radius of curvature of the exterior edge 128 willalways be greater than a corresponding radius of curvature of aninterior edge 130 FIG. 10C illustrates a blade 100 fabricated asdisclosed herein. In this variation, the blade 100 exterior shell 18 isformed with the body material 24 deposited within the shell 18.Accordingly, since the blade shell 18 is reinforced, a cutting edge 106formed by the exterior knife shell 18 has an exterior radius ofcurvature that is less than or equal to the interior radius ofcurvature.

Variations of the invention include an exterior knife shell 22 layer ofabout 1 micron thick. However, the invention may also contemplate layersthat are less than or greater than 1 micron. In one example, theexterior knife shell 22 may be 0.01 microns thick. Silicon-rich lowstress silicon nitride may be deposited by low pressure chemical vapordeposition (LPCVD) using ammonia, and dichlorosilane at 835 degrees C.Various other materials may be used in as the exterior knife shell 22.For example, stoichiometric Si₃N₄, silicon carbide, boron carbide, boronnitride, diamond, amorphous carbon, any hard material that can bedeposited as a thin film, as well as any combination of materials andany suitable ceramic, metal, mineral, crystalline, or plastic materialmay be used so long as such materials may form a blade edge as describedherein.

FIG. 11 illustrates filling of the mold formed by the exterior knifeshell 22 with a body material 24. For example, a slurry of glass frit(for example IP900-vwg from Ferro Corp) is spin applied on the wafer tofill, or partially fill, the exterior knife shell 22 mold cavities, aswell as coat the horizontal surface. Then the slurry is dried and fired(typically in oxygen at 950 degrees C. for 10 minutes) to melt the glassparticles and form a continuous film of glass which must then beannealed (e.g., 560 degrees C. for 30 minutes).

In an alternative construction, an epoxy fills the exterior knife shell22 mold so that the epoxy serves as the filler or body portion 24 forthe blade.

In any case, the material forming the body portion 24 will be rigid sothat it provides sufficient mechanical support for the thinner shell ofthe exterior knife shell 22.

As noted herein, the filler material may be a glass, epoxy,polycrystalline silicon, ceramic, glass-ceramic, silicon dioxide, orother material. It is noted that placement of the glass frit, (or otherfiller material) into the shell or exterior knife surface of the bladeallows fabrication of a knife where the outer cutting surface or cuttingedge will have a radius of curvature that is set by the fabricationprocess, which allows for a smaller radius of curvature (as compared toa cutting surface that is deposited on a body material). Accordingly,the radius of the outer cutting surface can be as small as themanufacturing process allows. In contrast, when depositing the cuttingsurface onto an existing body portion, the radius of curvature of thecutting edge will always be greater than the smallest possible radiusachievable manufacturing the body portion edge. In some variations ofthe invention, the hardness of the body portion will be selected to beless than a hardness of the shell/exterior blade portion.

In an alternate variation, the filler or body portion is not required tocompletely fill the shell of the mold. Instead, the filler/body portion24 can be a coating of sufficient thickness to provide the mechanicalsupport, required for a given application. Such a coating (e.g., ofglass or other material) can start at about 1 micron in thickness. Themaximum thickness can be anywhere up to the filling of the mold. Asnoted above, such coatings may be applied by any of the known methods ofdepositing material (e.g., sputtering, thermal evaporation, e-beamevaporation, low pressure chemical vapor deposition, etc). For example,in the above case of glass, films of this material can be convenientlydeposited by rf sputtering, or by thermal evaporation, usually followedby annealing (typically at about 560 C) to minimize stress.

FIG. 12 illustrates optionally bonding a wafer or substrate 26 (e.g.,Pyrex, or silicon) bonded on to the wafer assembly 1. If glass was usedas the filler body, then the bonding can be done by heating in a furnaceto 950 degrees C. for 10 minutes Alternatively the bonding can be donewith a film of epoxy between the glass wafer 26 and body filler 24. ThePyrex wafer may be thinned (typically by lapping) to any desiredthickness (typically about 100 microns). Alternatively the wafer can bethinned prior to step 11, although it must then be handled carefully toavoid breakage. In any case, the substrate may form a base for the knifeblade.

FIGS. 13-18 show an example of processing the wafer assembly 1 toextract a completed (but unshaped) knife blade 100.

FIG. 13 shows a cross sectional view of the assembly 1 after cuttinggrooves 50 (e.g., by a dicing saw) in the assembly 100. The grooves 50define the 4 sides (width and length) of the individual knife blades100.

FIG. 14 shows a wax-like material 52 applied to cover the horizontalsurface of the wafer 1 and rill the grooves 50. The wax-like material 52provides protection from the etchant to be used in the next step.

FIG. 15 illustrates softening the wax-like material and applying ahandle wafer 54 (e.g., pyrex or oxide coated silicon) onto the wax. Thenthe oxide and nitride layers are removed from the backside of the moldwafer (e.g., using lapping, grinding, or chemical etching, or plasmaetching).

FIG. 16 shows the wafer assembly 1 after removal of the silicon. Forexample, the wafer can be put into etchant such as aqueoustetramethylammonium hydroxide (e.g., 25 wt % TMAH in water, at 60degrees C.) to dissolve all of the silicon from the mold of the exteriorcutting surface 18 of the wafer assembly 1.

FIG. 17 illustrates the assembly after removal of any excess wax. Forexample, the excess wax can simply be heated up and melted enough thatthe individual knife blades 100 can be removed (as shown in FIG. 18).

FIG. 19A shows a perspective view of a knife 90 according to the presentinvention. As shown, a knife blade 100 is cleaned, and bonded to asupporting handle 108 (e.g., by reflowing glass frit, or by epoxy 110).

FIG. 19B shows an end view of the knife 90, the micro-machined knife mayhave a cross sectional area of a substantially pentagonal shape.However, other shapes are also possible. For example, the crosssectional shape may be trapezoidal, triangular, etc.

As shown in FIG. 19B, the micro-machined knife 90 includes a blade 100having a cutting surface 102 or shell located over body portion 104. Invariations of the invention, the cutting surface 102 comprises a hardmaterial as described herein. In additional variations, the body portion104 comprises a rigid material that provides sufficient support to thecutting surface to prevent deflection of the cutting surface. As aresult, the exterior thin cutting surface 102 on a knife may be lessprone to cracking or damage because of the rigid body portion. As notedabove, the cutting surface may comprise silicon nitride.

The blade edge 106 of the knife 100 is formed at the intersection of thetwo adjacent surfaces and may have a radius of curvature no greater than500 angstroms. As noted herein, because the blade edge 106 is formedprior to the body portion 104, the radius of the blade edge 106 may bethe smallest attainable radius given the processing limitations.

As noted above, the shell of the exterior cutting surface 102 may beformed within the etched channel of the substrate. After formation, thebody portion may be applied as a filler (e.g., epoxy or glass) withinthe cavity or channel. Variations of the invention include a bodyportion that is partially filled with the epoxy or glass. Alternatively,or in combination, a third material may be used behind the epoxy/glassto completely fill the shell 102.

The knife blade 100 may be designed to be clear or transparent to allowvisibility through the knife body. As such, the substrate or base 108may be constructed from a transparent material as well. In the exampleprovided above, the substrate comprises a glass wafer. In somevariations, the materials are transparent or deposited in a sufficientlythin layer that they are functionally transparent. Moreover, the handle108 may also be transparent.

FIG. 20 illustrates an example of the knife body having an end that issharpened. The opposite end is attached to a handle. The lappingrequired to produce the illustrated geometry can be performed prior todissolving the silicon. Shaping the knife body with the silicon in placeprovides mechanical support to the knife body.

In the configuration shown, the shell obtains mechanical support fromthe body filler material rather than the handle or any frame.Accordingly, in variations of the device, there is no need for a siliconframe as may be found with other conventional devices. This permitscomplete removal of the surrounding silicon during the fabricationprocess. The removal of any frame structure makes it easier to processthe blade into various other geometries (e.g., as shown in FIG. 20 wherethe handle 108 is affixed to the end of the blade 100 while the oppositeend is sharpened to a point).

In certain cases, a body filling (or lining) material can be initiallyapplied as a liquid (e.g., epoxy), or can become liquid duringprocessing (e.g., melting glass). In such a case, the liquid materialmust wet the inside surface of the knife shell (where “wet” means thatthe liquid is attracted to the surface and spreads out on it). Notwetting means that the liquid does not spread out to cover the surfacebut typically beads up. For example: molten pyrex glass does not wetlpcvd silicon rich silicon nitride. In such cases, it may be necessaryto apply a surface treatment to assist in the wetting process given thechosen body filling material. One example of a surface treatment thatimproves wetting by molten glass is the application of a thin film ofalumina. A convenient way to apply the alumina is to evaporate orsputter aluminum (typically 100 to 1000 angstroms thick), and then heatit in oxygen (air is sufficient) to a temperature sufficient tocompletely oxidize the aluminum (e.g., 500 C). Wetability is determinedby the chemical composition and the microscale roughness of the surface.Typically, a smooth surface is harder to wet while a rough surface iseasier to wet. Note that all of the materials in this example (siliconnitride, alumina, and glass) are transparent. Accordingly, for thoseapplications described above, where transparency is desired, the wettingagent shall be transparent as well.

1. A. micro-machined knife comprising; an interior body portioncomprising a body material, the body portion having at least a first andsecond sides which intersect to form an interior edge having an interiorradius of curvature; an exterior knife shell located exterior to atleast the first and second sides of the interior body portion, theexterior knife shell comprising a shell material; and a cutting edgeformed by the exterior knife shell and exterior to the interior edge,the cutting edge having an exterior radius of curvature, where theexterior radius of curvature is less than or equal to the interiorradius of curvature.
 2. The micro-machined knife of claim 1, wherein theexterior radius of curvature is no greater than 500 angstroms.
 3. Themicro-machined knife of claim 2, wherein the exterior radius ofcurvature is no greater than 100 angstroms.
 4. The micro-machined knifeof claim 3, wherein the exterior radius of curvature is no greater than50 angstroms.
 5. The micro-machined knife of claim 4, wherein theexterior radius of curvature is no greater than 25 angstroms.
 6. Themicro-machined knife of claim 5, wherein the exterior radius ofcurvature is between 5 and 25 angstroms.
 7. The micro-machined knife ofclaim 1, further comprising a substrate located on a portion of theinterior body portion.
 8. The micro-machined knife of claim 7, where thesubstrate is substantially transparent.
 9. The micro-machined knife ofclaim 1, where the body material comprises a material selected from thegroup consisting of an epoxy and a glass.
 10. The micro-machined knifeof claim 1, where the shell material comprises a material selected fromthe group consisting of silicon nitride, silicon rich silicon nitride,silicon carbide, diamond, boron carbide, boron nitride.
 11. Themicro-machined knife of claim 1, further a base substrate attached to aportion of the body located opposite to the cutting edge.
 12. Themicro-machined knife of claim 1, where the exterior knife shell isapproximately 1 micron thick.
 13. The micro-machined knife of claim 1,further comprising a handle attached to a portion of the interior body.14. The micro-machined knife of claim 1, where a first end of theinterior body forms a point.
 15. The micro-machined knife of claim 1,where a cross sectional area of the interior body portion and exteriorknife shell comprises a substantially pentagonal shape.
 16. Themicro-machined knife of claim 1, where the body material issubstantially transparent.
 17. The micro-machined knife of claim 1,where the shell, material is substantially transparent.
 18. Amicro-machined knife blade comprising; a body shell having at least twosides; a cutting edge formed by an intersection of the two sides, wherea radius of the cutting edge is no greater than 500 angstroms; where thebody shell comprises a shell material; and a body filler located betweenthe two sides.
 19. The micro-machined knife of claim 18, where the bodyfiller comprises a body edge adjacent to the cutting edge, where theradius of curvature of the cutting edge is less than or equal to aradius of curvature of the body edge.
 20. The micro-machined knife ofclaim 18, wherein the radius of curvature is no greater than 100angstroms
 21. The micro-machined knife of claim 18, wherein the radiusof curvature is no greater than 50 angstroms.
 22. The micro-machinedknife of claim 18, wherein the radius of curvature is no greater than 25angstroms.
 23. The micro-machined knife blade of claim 18, where thebody shell is open on each end.
 24. The micro-machined knife blade ofclaim 18, where the body filler substantially fills the body shell. 25.The micro-machined knife blade of claim 18, where the body fillerpartially fills the body shell.
 26. The micro-machined knife blade ofclaim 25, further comprising a third material which substantially fillsthe body shell.
 27. The micro-machined knife blade of claim 18, furthercomprising a substrate located on a side of the body shell opposite tothe cutting edge.
 28. The micro-machined knife blade of claim 18,further comprising a substrate bonded to the body filler on a side ofthe micro-machined knife blade opposite to the cutting edge.
 29. Themicro-machined knife blade of claim 18, where the body shell material issubstantially transparent.
 30. The micro-machined knife blade of claim18, where the body filler is substantially transparent.
 31. Themicro-machined knife blade of claim 18, where the body filler comprisesa material selected from the group consisting of a glass, epoxy,polycrystalline silicon, ceramic, glass-ceramic, and silicon dioxide.32. The micro-machined knife blade of claim 18, where the body shellmaterial comprises a material selected from the group consisting ofsilicon nitride, silicon rich silicon nitride, silicon carbide, diamond,boron carbide, boron nitride.
 33. The micro-machined knife blade ofclaim 18, where the body shell is approximately 1 micron thick.
 34. Themicro-machined knife blade of claim 18, where a first end of body shellforms a point.
 35. The micro-machined knife of claim 18, where a crosssectional area of the interior body portion and exterior knife shellcomprises a substantially pentagonal shape.
 36. A wafer assembly forcreating a plurality of micro-machined knife blades, the assemblycomprising: a first wafer material having a surface; a plurality ofknife mold pits etched into the surface of the first wafer material,where the plurality of knife mold pits comprise at least two surfaces,where the intersection of surfaces forms an edge having a radius ofcurvature no greater than 500 angstroms; a blade shell materialdeposited into the knife mold pits and at least partially deposited ontothe surface of the first wafer material; and a filler material depositedonto the blade shell material and at least partially filling knife moldpits.
 37. The wafer assembly of claim 36, wherein the radius ofcurvature is no greater than 100 angstroms.
 38. The wafer assembly ofclaim 36, wherein the radius of curvature is no greater than 50angstroms.
 39. The wafer assembly of claim 36, wherein the radius ofcurvature is no greater than 25 angstroms.
 40. The wafer assembly ofclaim 36, where the first material comprises a (100) silicon wafer. 41.The wafer assembly of claim 36, further comprising a sharpening layerbetween the knife mold pits and the blade shell material.
 42. The waferassembly of claim 41, where the sharpening layer comprises silicondioxide.
 43. The wafer assembly of claim 36, where the filler materialsubstantially fills each of the knife mold pits.
 44. The wafer assemblyof claim 36, where the filler material partially fills each of the knifemold pits.
 45. The wafer assembly of claim 44, further comprising athird material which substantially fills each of the knife mold pits.46. The wafer assembly of claim 36, further comprising a substratelocated on at least a portion of the wafer surface.
 47. The waferassembly of claim 36, where the blade shell material is substantiallytransparent.
 48. The wafer assembly of claim 36, where the fillermaterial is substantially transparent.
 49. The wafer assembly of claim36, where the filler material comprises a material selected from thegroup consisting of a glass, epoxy, polycrystalline silicon, ceramic,glass-ceramic, and silicon dioxide.
 50. The wafer assembly of claim 36,where the blade shell material comprises a material selected from thegroup consisting of silicon nitride, silicon rich silicon nitride,silicon carbide, diamond, boron carbide, boron nitride.
 51. The waferassembly of claim 36, where the blade shell material is approximately 1micron thick.
 52. A method of preparing a micro-machined surgical blade,the method comprising: etching a pattern of elongate channels in asurface of a wafer material, where each channel has at least one edge;coating the channels by depositing a blade shell material into thechannels and at least partially covering the surface of the wafermaterial; at least partially filling the coated channels with a fillermaterial; bonding a substrate to the top of the filler material;creating grooves in the wafer material to define a size of themicro-machined surgical blade; and removing the remaining wafer materialto separate the micro-machined surgical blade from an adjacentmicro-machined surgical blade, where each micro-machined surgical bladecomprises the blade shell material covering the filler material, and thesubstrate, and where each micro-machined surgical blade has a blade edgecorresponding to the edge of the elongate channel.
 53. The method ofclaim 52, where the blade edge comprises a radius of no greater than 500angstroms.
 54. The method of claim 52, wherein the radius of curvatureis no greater than 100 angstroms.
 55. The method of claim 52, whereinthe radius of curvature is no greater than 50 angstroms.
 56. The methodof claim 52, wherein the radius of curvature is no greater than 25angstroms.
 57. The method of claim 52, where the wafer materialcomprises (100) single crystal silicon.
 58. The method of claim 52,where the blade shell material comprises a material selected from thegroup consisting of silicon nitride, silicon rich silicon nitride,silicon carbide, diamond, boron carbide, boron nitride.
 59. The methodof claim 49, where coating the channels by depositing silicon nitridecomprises depositing a thickness of about 1 micron of silicon nitride.60. The method of claim 52, where the filler material comprises amaterial selected from a glass, epoxy, polycrystalline silicon, ceramic,glass-ceramic, and silicon dioxide.
 61. The method of claim 52, furthercomprising depositing a sharpening layer on the channels and wafermaterial prior to coating the channels with the blade shell.
 62. Themethod of claim 61, where depositing the sharpening layer comprisessilicon dioxide.
 63. The method of claim 61, where the sharpening layeris less than about 1 micron in thickness.
 64. The method of claim 52,further comprising bonding a handle to the micro-machined surgicalblade.
 65. The method of claim 52, further comprising shaping an end ofthe micro-machined surgical blade to form a knife tip.
 66. The method ofclaim 52, where the blade shell material is substantially transparent.67. The method of claim 52, where the filler material is substantiallytransparent.
 68. The method of claim 52, where the substrate issubstantially transparent.